Foto: argus/ Maik Schröder mit freundlicher Genehmigung des Instituts für Mikrotechnik Mainz GmbH Quelle: DLR Göttingen Quelle: DLR Göttingen
Physik im Kontext
What are X-Rays
Röntgen's Discovery
History of Radiology
X-Ray Production
X-rays & Matter
Detection Issues
Detection Methods
Background: Fluorescence

Physics & the Detection of Medical X-Rays

Fluoroscopy enables a physician or other health care provider to look into the body and watch changes in real time. As its name indicates fluoroscopy relies on the process of fluorescence to provide these pictures. Thus, your students should study the basic process of fluorescence before studying the concepts discussed below.

The old-fashioned way to provide the images for fluoroscopy is to use a copper activated zinc cadmium sulfide phosphor. This material is used in many different phosphorescent materials and is responsible for the yellow-green visible light which is seen in many dark areas. When x-rays strike a zinc sulfide compound, the material converts x-rays directly to a yellow-green visible light. The patient stands between the source of the x-rays and the screen. As the x-rays pass through the patient some are absorbed, the result is that those x-rays that reach the screen cause light to be emitted. Thus, the physician can see just as he/she could see inside the body with film.

The process is rather inefficient with only a few percent of the x-ray photons actually creating visible light. Thus, the dosage required for medical analysis is rather high. The result can be very unhealthy for the patient.

The fluoroscope was invented in 1896 by Enrico Salvioni. The name was coined by Thomas Edison when he created a machine in same year. Edison used calcium tungstate as the fluorescing material. Unfortunately, he quickly discovered the health hazard related to the fluoroscope. Edison and his assistant, Clarence Dally were exposed to large doses of x-rays frequently because they were demonstrating the fluoroscope. The damage to Mr. Dally’s body was so sever that in 1904 he died of cancer which was a result of the exposure. Edison stopped his investigations and developments of x-ray related devices as a result of his assistant’s death. A positive result of this tragedy was that people began to take seriously the hazards of x-rays.

Today, the risks of over exposure are greatly reduced through the use of image intensifiers. As with film, the multiple step process enables researchers to obtain high quality images with a very small dose. First, the x-rays strike fluorescent materials and stimulate the creation of visible light photons. These photons, in turn, create cause electrons, commonly called photoelectrons, to be emitted by a second material. The electrons travel in a vacuum and are focused by a series of electrodes on a screen. Frequently this screen is some type of video camera which can then be connected to a monitor and/or a recording device. By using this type of system the intensity of x-rays can be greatly reduced while the image intensity is 100s of times better than directly exposing the fluorescent screen.

Glow in the Dark
An experiment which children can do to create a glow-in-the-dark material

Another recipe for glow-in-the-dark material

A very short history of the process.

An article about the basic process with many links to other related articles.

Medical Devices: Fluoroscopy
A short description but tow nice images of circa 1918 fluoroscopic devices.  Scan down the page until you get to Fluoroscopy.

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In cooperation with
Modern Miracle Medical Machines
Physics Education Research Group
Kansas State University